The present invention relates to a shift actuator for a transmission, which actuates, in a direction of shift, a shift lever of the transmission mounted on a vehicle.
As the shift actuator for a transmission, which actuates, in a direction of shift, a shift lever of the transmission, there has been generally used a fluid pressure cylinder that utilizes the fluid pressure such as air pressure or hydraulic pressure as a source of actuation. The shift actuator using the fluid pressure cylinders requires a piping for connecting the source of fluid pressure to the actuators, an electromagnetic change-over valve for changing over the flow passage of the operation fluid, and space for the arrangement thereof, resulting in an increase in the weight of the device as a whole.
In recent years, there has been proposed an actuator constituted by an electric motor as a shift actuator for a transmission mounted on a vehicle which is provided with neither a source of the compressed air nor a source of the hydraulic pressure. The shift actuator constituted by the electric motor needs neither the piping for connection to the source of fluid pressure nor the electromagnetic change-over valve, unlike the actuators that use fluid pressure cylinders, and can, hence, be constituted in a compact size as a whole and in a reduced weight.
The actuator using an electric motor needs a speed reduction mechanism for obtaining a predetermined actuating force. As the speed reduction mechanism, there have been proposed the one using a ball-screw mechanism and the one using a gear mechanism. However, the actuators using the ball-screw mechanism and gear mechanism are not necessarily satisfactory in regard to the durability of the ball-screw mechanism and the gear mechanism and in regard to the durability and the operation speed of the electric motor.
It is an object of the present invention to provide a shift actuator for a transmission, which features excellent durability and a high operation speed.
In order to achieve the above-mentioned object according to the present invention, there is provided a shift actuator for a transmission, which actuates, in a direction of shift, a shift lever of the transmission, the shift actuator comprising:
an operation rod that engages with an operation member linked to the shift lever;
a magnetic moving means disposed on the outer peripheral surface of the operation rod;
a cylindrical fixed yoke surrounding the magnetic moving means; and
a pair of coils arranged on the inside of the fixed yoke neighboring in the axial direction.
The magnetic moving means comprises a moving yoke mounted on the outer peripheral surface of the operation rod, and an annular permanent magnet mounted on the outer peripheral surface of the moving yoke and having magnetic poles in the outer peripheral surface and in the inner peripheral surface thereof, and the moving yoke has a cylindrical portion on which the permanent magnet is mounted and annular flanges formed at both ends of the cylindrical portion, the outer peripheral surfaces of the flanges being constituted to be located close to the inner peripheral surface of the fixed yoke.
Further, the magnetic moving means comprises an intermediate yoke mounted on the outer peripheral surface of the operation rod, a pair of annular permanent magnets disposed each on both sides of the intermediate yoke to hold it therebetween and having magnetic poles in both end surfaces thereof in the axial direction, and a pair of moving yokes disposed each on the outer sides of the pair of permanent magnets in the axial direction thereof, and the pair of moving yokes has annular flanges which are so constituted that the outer peripheral surfaces of said moving yokes are located close to the inner peripheral surface of said fixed yoke.
It is desired that the pair of permanent magnets have their opposing end surfaces magnetized into the same polarity.